Raman spectroscopy of graphite intercalation compounds: Charge transfer, strain, and electron–phonon coupling in graphene layers

Abstract

Graphite intercalation compounds (GICs) are an interesting and highly studied field since 1970's. It has gained renewed interest since the discovery of superconductivity at high temperature for CaC 6 and the rise of graphene. Intercalation is a technique used to introduce atoms or molecules into the structure of a host material. Intercalation of alkali metals in graphite has shown to be a controllable procedure recently used as a scalable technique for bulk production of graphene, and nano-ribbons by induced exfoliation of graphite. It also creates supra-molecular interactions between the host and the intercalant, inducing changes in the electronic, mechanical, and physical properties of the host. GICs are the mother system of intercalation also employed in fullerenes, carbon nanotubes, graphene, and carbon-composites. We will show how a combination of Raman and ab-initio calculations of the density and the electronic band structure in GICs can serve as a tool to elucidate the electronic structure, electron-phonon coupling, charge transfer, and lattice parameters of GICs and the graphene layers within. This knowledge of GICs is of high importance to understand superconductivity and to set the basis for applications with GICs, graphene and other nano-carbon based materials like nanocomposites in batteries and nanoelectronic devices.

Superconductivity in graphite intercalation compounds

“…While this model is now has strong experimental support, interesting inconsistencies remain, for example the reported calcium isotope effect [43]. Furthermore the large electron-phonon coupling between * electrons and Cxy phonons measured in ARPES [51,52], is in contrast with DFT predictions despite being consistent with linewidths measured in Raman Spectroscopy [50,65], an effect also shown to evolve in monolayer and few layer graphene with increasing doping [66]. However despite these interesting discrepancies more recent ARPES reconcile the picture arising from DFT [54,45].…”

A Guide to and Review of the Use of Multiwavelength Raman Spectroscopy for Characterizing Defective Aromatic Carbon Solids: from Graphene to Amorphous Carbons

“…The denomination n-stage GICs can be found in [268], n defining the constant number of graphene layers between any nearest pair of intercalant layers. More details about the staging can also be found in [266]. The diminution of the interlayer spacing distance reduced the van der Waals interaction between planes so that it can be envisaged as a route to form graphene and nano-ribbons [269].…”

“…The diminution of the interlayer spacing distance reduced the van der Waals interaction between planes so that it can be envisaged as a route to form graphene and nano-ribbons [269]. The list of metals and small molecules that can be embedded in between graphene planes is huge and not exhaustive here: Alkali-metals (K, Li, Cs, Rb); alkali-earth-metals (Be, Ca, Ba); halogens; C 60 [270] [266,273]. Superconductivity has been observed in many GICs (with the highest critical temperature found at a relatively high temperature, 11.5 K, for CaC 6 , see references [266]) and multiwavelength Raman spectroscopy is a central characterization tool because superconductivity may be due to electron-phonon interaction and mediated by phonons [276].…”

“…The list of metals and small molecules that can be embedded in between graphene planes is huge and not exhaustive here: Alkali-metals (K, Li, Cs, Rb); alkali-earth-metals (Be, Ca, Ba); halogens; C 60 [270] [266,273]. Superconductivity has been observed in many GICs (with the highest critical temperature found at a relatively high temperature, 11.5 K, for CaC 6 , see references [266]) and multiwavelength Raman spectroscopy is a central characterization tool because superconductivity may be due to electron-phonon interaction and mediated by phonons [276]. Multiwavelength Raman spectroscopy also allows a direct measurement of the Fermi level by observing the Pauli blocking (which results in the 2D band intensity vanishing by tuning the wavelength of the laser) [271].…”

“…[266] and references therein): Graphite intercalated compounds (GICs). GICs are multilayered materials sufficiently ordered to exhibit staging in which the number of graphitic layers in between adjacent intercalants can be varied in a controlled way.…”